The connection between a pipe carrying a fluid and a user device is typically effected by a coupling member consisting of a single insert or of an insert with an associated appropriately shaped swivel nut.
In a connection made with a single insert, one end of the insert is connected to the pipe while the other is provided with a shank that screws into a seat on the user device.
When making the connection with an insert and a swivel nut, one end of the insert is connected to the pipe while the other end is connected to the swivel nut. In this version of the coupling member, the swivel nut is provided with a threaded shank that screws into the seat on the user device.
The sealing system, in both the insert-type connection and in the insert with swivel nut-type connection prevents fluid leaking out through the threaded connection formed between the shank of the coupling member and the seat of the user device, especially when the threaded connection is not fluidtight. This is particularly the case when using coupling members with shanks provided with a short thread.
The current tendency is to use threads characterized by having little length in the direction of the axis of the shank (longitudinal direction). This tendency is due to the increasing use of “universal” threads generated by the envelope of two standard conical profiles (for example, the envelope of a BSPT profile and an NPTF profile, which are much used in hydraulics and pneumatics).
The “universal” threads are well known to be shorter than normal standard threads. This is to allow generation of the envelope on which they are based.
The “universal” thread does not produce a fluid-tight connection between the flanks of the thread of the shank and those of the thread of the seat. The sealing system therefore assumes a fundamental importance in the functionality of the connection.
Generally speaking, sealing systems use a sealing ring to act as a physical obstacle to the escape of fluid into the external environment.
A practical example of a sealing system with a sealing ring for making couplings with a threaded shank used in hydraulic or pneumatic applications is disclosed in U.S. Pat. No. 5,441,314.
The above patent discloses a sealing system that uses a groove in the vicinity of the threaded shank, at the opposite end to the end of the shank. The groove contains a PTFE (polytetrafluoroethylene) sealing ring that has conical side walls and is shaped so as to fit the walls of the groove.
It is known, however, that the manufacture and inspection of sealing rings that have conical side walls can present some difficulties, which increases the costs of manufacture.
High productivity for PTFE sealing rings is ensured by lathe turning, which can only be done with great difficulty to produce conical sealing rings.
Moreover, to inspect a conical sealing ring, as must be done to ensure stable fitting of the ring in its groove, requires measuring two diameters and one thickness, or one diameter, one length and one cone angle. This greatly increases inspection times.
There is therefore an awareness of the need to provide high productivity sealing systems with sealing rings which, at the same time, will ensure that the ring is a good fit in its groove.
The problem addressed by the present invention is that of devising a sealing system with a sealing ring in which the structural and functional characteristics are such as to fulfil the abovementioned needs and at the same time obviate the disadvantages indicated with reference to the prior art.